It was my impression when it was added that the Series entity was meant to track officially curated and published series of release groups, releases, works, etc. However, there are a few series floating around MB that are more like collections than series, e.g. Target CDs and Purple Vinyl.
I noticed that Style/Series hasn’t been updated in ages, so it doesn’t give much guidance on this type of scenario. Should the Series entity be used for something so nebulous, or is it pretty much anything goes?
(Full disclosure: I’ve never attempted to put together a collection, so I have no idea if multiple editors can contribute to one or not.)